1. Field of the Invention
The present invention relates to an electronic device test system for testing semiconductor integrated circuit chips or other various types of devices under tests (hereinafter referred to representatively as “DUTs”).
2. Description of the Related Art
In an electronic device test system referred to as a “handler”, a large number of DUTs carried on a customer tray are conveyed to the inside of the handler. There, each DUT is picked up by a contact arm and brought into electrical contact with a contact part of a test head. The tester inputs a test pattern to the DUT for operation and examines the response pattern. Further, when finishing this test, each DUT is ejected from the contact part of the test head and reloaded on a tray in accordance with the test results so as to thereby classify it into a good device or defective device or high speed, medium speed, or low speed device.
Among these handlers, as a handler used for logic type ICs with a relatively short test time, for example, there is the one disclosed in Japanese Patent Publication (A) No. 2001-33514. This type of handler is a handler of a type which picks up two DUT's by a contact arm and simultaneously pushes them against contact parts. For a high temperature test, a heat plate is used to heat the DUTs and a heater is built into the contact arm to supply heat energy to the picked up DUTs for the test.
In this handler, to raise the test efficiency, it may be considered to simultaneously measure four, eight, or 16 DUTs.
However, for example, if simultaneously picking up four DUTs and simultaneously pushing these against contact parts for testing, there were the following problems.
First, when loading a handler with a lot unit of DUTs, the general practice has been to finish the lot, then load the next lot of DUTs, but if the number of DUTs in a lot is not a whole multiple of four, the last group of DUTs of the lot become one to three DUTs. For this reason, at the last test, some of the pickup devices of the contact arm will push against the contact parts in a state with no DUTs. Further, when a customer tray is emptied of DUTs, the same situation occurs as with the end of a lot, so “the end of a lot” includes the case where a tray is emptied of DUTs.
Further, the DUTs are physically pushed against the contact parts of the test head for contact. The resultant wear makes it necessary to perform maintenance on some of the four contact parts in some cases. In such cases, the contact parts requiring maintenance are turned off (so no test patterns are sent from the tester) and only the usable contact parts are used for line operation.
Further, the pretest DUTs are moved by a three-dimensional pick-and-place system from a customer tray to a heat plate and are further moved by another three-dimensional pick-and-place system from the heat plate to a buffer stage. The DUTs of this buffer stage art picked up by a contact arm and pushed against the contact parts. Pickup failure of DUTs or other trouble before being picked up by a contact arm sometimes results in four DUTs not being properly held.
In each case, the DUTs are pushed against the contact parts in a state with some missing as compared with the regular simultaneous measurement of four DUTs, so the balance of the pushing pressures is lost, the pushing surfaces become skewed, and the positional relationships between the terminals of the DUTs and the terminals of the corresponding sockets are easily thrown off—resulting in unnecessary stress to the terminals of the sockets or poor contact and a consequent drop in the test quality. The terminals of the sockets come into contact with DUTs hundreds of thousands of times during their service lives, so reliability of contact is required. Further, a heating source and/or cooling source provided at the contact arm is used to maintain the DUTs at a predetermined temperature, but if the pushing surface of the contact arm and the receiving surface of a DUT become skewed and the heat conduction with the DUT deteriorates, the test is liable not to be able to be conducted under the target temperature conditions.